1. Field of the Invention
The present invention relates to a three-dimensional (3-D) display capable of viewing three-dimensional images without using special glasses.
2. Description of the Prior Art
As a method of displaying three-dimensional images without using glasses, a lenticular method and a parallax barrier method have been conventionally proposed.
The parallax barrier method is a method in which a parallax barrier comprising slits is arranged short of a display screen to cause parallax, to obtain three-dimensional images. FIG. 34 is a structural drawing for explaining the principle of a conventional 3-D display by a parallax barrier method.
Left eye pixels L having left eye image information and right eye pixels R having right eye image information are alternately formed horizontally in a display screen 200. A parallax barrier plate 300 having slits 300a transmitting light from the pixels L and R and barriers 300b screening the light alternately formed in a slit shape horizontally therein is arranged ahead of the display screen 200.
A light beam L1 directed toward the left eye EL of a observer out of light beams emitted from the left eye pixel L passes through the slit 300a, to reach the left eye EL, while a light beam L2 directed toward the right eye ER of the observer is screened by the barrier 300b. Further, a light beam R1 directed toward the right eye ER of the observer out of light beams emitted from the right eye pixel R passes through the slit 300a, to reach the right eye ER, while a light beam R2 directed toward the left eye EL is screened by the barrier 300b.
Consequently, only the light beams L1 from the left eye pixels L are incident on the left eye EL of the observer, while only the light beams R1 from the right eye pixels R are incident on the right eye ER. At this time, there is sufficient parallax information for a human being to perceive three-dimensional images by parallax between his or her eyes between the light beams L1 from the left eye pixels L and the light beams R1 from the right eye pixels R. Therefore, the observer can enjoy three-dimensional images.
In the 3-D display by a parallax barrier method, however, the light beams L2 and the light beams R2 from the pixels L and R are screened by the barriers 300b, whereby the amounts of light incident on the left and right eyes EL and ER of the observer are small, to darken the display screen 200.
Furthermore, if a general liquid crystal display (LCD) panel having a pixel pitch of approximately 0.1 mm is used for the display screen 200, the spacing between the slits 300a, that is, a barrier pitch in the parallax barrier plate 300 is approximately 0.2 mm in the conventional 3-D display by a parallax barrier method shown in FIG. 34.
On the other hand, there is a 3-D display capable of obtaining three-dimensional images in a wide range by constituting a display screen by a plurality of (more than two) columns of pixels, that is, a 3-D display of a multi-viewpoints type autostereoscopic. A barrier pitch in a case where the number of viewpoints is n in this multi-viewpoints type autostereoscopic 3-D display, that is, in the case of an n-viewpoints type autostereoscopic 3-D display is approximately (0.1.times.n) mm. In the conventional 3-D display by a parallax barrier method, the larger the value of n becomes, the more easily the barriers 300b in the parallax barrier plate 300 is recognized as vertical stripes.
Furthermore, a surface of the parallax barrier plate 300 on which the barriers 300b exist and the display screen 200 must be spaced apart from each other so as to view three-dimensional images. If the eyes of the observer are focused on the barriers 300b in the parallax barrier plate 300, therefore, it is impossible to satisfactorily view three-dimensional images.
Furthermore, as a method causing parallax to obtain three-dimensional images by the same function as that in the above described parallax barrier method, a method changing a light source into a slit light source is disclosed in U.S. Pat. No. 4, 717, 949, U.S. Pat. No. 4,829,365, U.S. Pat. No. 5,036,385, and U.S. Pat. No. 5,040,878. This method is a method of separating light beams incident on the left eye and the right eye of a observer by forming a light source in a stripe shape, in which three-dimensional images can be enjoyed without arranging anything in an image display portion on the side of the observer. The 3-D display disclosed in the above described patent uses as a light source "a flat screen in a plane shape having a plurality of limited light radiating portions separated from each other with regular spacing displayed along its surface and being dark between the radiating portions".
Examples of the above described light source include a light source of a spontaneous light type utilizing a fluorescent gas used for a fluorescent light tube packed in a thin groove of glass obtained by etching, a wire filament such as tungsten emitting light by thermal excitation when a current is caused to flow, for example, or an electron emitting material emitting light by excitation and non-excitation of electrons when an AC current is caused to flow and a light source of a projection type passing a laser beam through a diffraction grating and projecting an objective line on the reverse surface of a translucent sheet (a surface on the opposite side of a light valve).
In the above described 3-D display by a stripe light source method, however, it is impossible to bring a light emitting portion into close contact with the image display portion with respect to the light source of a spontaneous light type, whereby the viewing distance becomes very large. On the other hand, the 3-D display is not only increased in size but also complicated in construction with respect to the light source of a projection type.
Furthermore, in the 3-D display by a lenticular method, the wall thickness of a lenticular lens method is large. If a pixel pitch in a display screen is decreased, therefore, a proper viewing position where light beams from pixels are gathered on the left and right eyes of a observer is far from the display screen.
If the display screen is constituted by a display screen having black matrix portions, for example, an LCD panel, regions corresponding to the black matrix portions are also formed in the proper viewing position. Even if the observer slightly moves his or her head, therefore, the observer cannot view three-dimensional images because the eyes of the observer are positioned in the regions corresponding to the black matrix portions so that the display screen is darkened.